Motor controller



ori inal Filed Ma 24, 1934 Reissue Feb. 11, 1936 UNITED. STATES PATENT OFFICE- Moron oon'raonma Carroll Stansbury, Wauwatosa, Wis., asaignor to Cutler-Hammer, Inc., Milwaukee, 71s., a corporation of Delaware 8 Claims.

This invention relates to control systems and more particularly to regulating systems for controlling the speed of motors.

Among the objects of the invention is the provision of means for maintaining the speed. of motors constant at any desired preselected value.

Another object is to provide a speed controlling device of the aforementioned character employing electronic tubes to perform the regulating and controlling functions.

Another object is to provide a controller which permits of accurate speed control of a motor under widely varying load conditions.

Another object is to provide a controller which aiTords accurate speed control under rapidly varying load conditions.

Another object is to provide a controller which accomplishes the aforementioned results when the motor operates at a relatively low speed.

Another object is to provide a controller which has no mechanically moving elements which are required to respond to the controlling impulses.

Another object is to provide a controller which requires no arc interrupting contacts to open and close circuits of high voltage or magnitude.

Another object lsto provide a controller which is rapid and accurate in response to changes in operating conditions.

Other objects and advantages will hereinafter appear,

As is well known, the speed of alternating current motors may be varied by .varying the impedance oi the primary or of the secondary circuit- Various means have been proposed for the variation of such impedance, one 01 such means consisting of connecting in series with a winding of the motor a so-called saturable reactor in which the impedance of a coil connected in an alternating current circuit is variedby superimposing upon the flux created by the alternating current flowing in said coil a. direct current flux induced in the same magnetic structure by a unidirectional current flowing .in another coil.

The use of such a saturable reactor is particularly advantageous where large powers have to be controlled, since a very small amount or energy in the direct current circuit will supply a controlling eflect sufllcient ior controlling a very large motor. In the present system, automatic meanshave been provided whereby tendencies oi an' induction motor to depart from a desired speed immediately affect an electronic tube which, in turn, instantaneously varies the direct current oi the saturable reactor to thereby vary the motor characteristic to thus check departures oi the motor speed from the desired'value substantially in their incipiency.

The accompanying drawing is illustrative of one type of system embodying my invention.

In the drawing, lines L 1.. and L designate the terminals or a three phase alternating current supply system, I is a'three phase slip ring type induction motor having a primary winding terminating in the terminals I", I, i and secondary windings terminating in the slip rings I", l and I. Connected in series with the secondary winding is a saturable reactor 2 having alternating current coils 2', 2 and 2, which are connected in star between the slip rings I, I and I, respectively. The reactor also has a direct current coil 1. A gaseous electron tube 3 having a cathode 3, an anode 3" and a grid 3 has its cathode connected to the line L while the anode 3 is connected to the anode 4" of a rectitier 4 whose cathode 4 is connected to the line LP. The direct current winding 2 is connected in parallel with the rectifier l.

The system further includes a transformer 5 having a primary winding 5" which isconnected across the lines L and L and a secondary winding 5' which is connected in series with a condenser li across the terminals of a resistor I. The terminal 01' the resistor l which is common with-the condenser 6 is also connected to the grid 3. 8 is a full wave rectifier having a cathode 8' and anodes l and 8. A transformer 9 has its primary winding 9" connected across lines L and 1:". The secondary winding 9 of transi'ormer winding 9 has one end connected to the anode I" while its other end is connected to the common terminal of the resistor I and the winding 5''. Between this latter terminal and the cathode 8* are connected a condenser and in parallel therewith a resistor i2. A third transformer II) has a primary winding it! which is connected in shunt with a potentiometer resistor IS, the latter being connected across the coil 2 while its secondary winding between the line L and the anode 8. A condenser ll and a parallel resistor ll are connected between the line L and the cathode B.

The system operates in the following manner:

When the lines LL12 and L are energized the primary winding oi motor i receives current and a voltage is induced in the secondary circuit so that a current flows through the windings 2-, 2 and 2 of-the saturable reactor. The current Ill is connected through these windings depends upon the energization of the winding 2", the impedance of the windings 2', 2 and 2 increasing with decreasing current in the winding 2*. In other words, the higher the current in the winding 2 the lower will be the impedance of the secondary cirvoltage across the resistor I, the condenser ii and the condenser l3,the three being in series. The voltage across the resistor 1 is a function of the voltage induced in the secondary winding 5 of the transformer 5 whose primary is connected across the lines L and L The condenser H is charged by a voltage impressed upon it by the secondary winding 9' of the transformer 9 through the electron tube 8, said voltage being proportional to the line voltage. The eifective voltage of the condenser II is determined by the value of the resistance II. By proper adjustment of this resistance and the condenser H the effective voltage of the latter will attain a certain desired value at a given moment during the positive half cycle.

A voltage opposite to that of condenser II is impressed upon the condenser ll through the secondary winding l0" of the transformer i0 whose primary winding Iii is connected to the coil 2 of the reactor through potentiometer II. This voltage is a function of the adjustment, of the resistor l4 and of the condenser l3 and of the motor speed.

By varying the adjustment of the potentiometer I! to which is connected the primary winding iii of the transformer III the voltage impressed upon the winding lt can be adjusted with respect to the relatively fixed voltage which is the resultant of that of the condenser II and impedance 1 so that the critical value of the grid voltage is attained during any desired moment of the positive half cycle ofthe voltage impressed upon tube I and thus the strength of the current which is passed by the tube and which flows throughthe winding 2 may be adjusted.

If for a given adjustment of the potentiometer Ii the motor should slow down due to changes in load its secondary voltage increases thereby increasing the voltage impressed upon the condenser II and making the grid 1 more positive. This increases the effective current through the V coil 2' which, in turn, decreases the impedance of the coils 2-, 2? and 2 and causes the motor to speed up.

The rectifier 4 which is with the coil 2 to smooth connected in parallel out the oscillations of the current flowing therein in a well known mannor may be omitted under certain conditions.

Itwill thusbeseen that foranygiven adjust-.

ment of the potentiometer II the system tends to maintain the speed of the motor constant. and that this speed may be varied between substantially zero and synchronous speed of the motor. u While I have shown the invention in connecon be obvious to one skilled be used with -other intheartthat itmav mofmotorsandthat thereactorlmyheeonnectedto either thepri-- maryorsecondaryeircuitofsuchmotors.

Whatlclaimasnewanddesireto Letterslatentis:

with a wound rotor induction motor, itwill' secureas said means comprising means to supply a unidirectional reference voltage to said grid, also means to supply a second unidirectional voltage to said grid which is a function of said char acteristic of said machine and which is opposed to said reference voltage, and also means connected to said alternating current supply to superimpose an alternating voltage of a given phase relative to the voltage of said supply upon the resultant of said reference voltage and said second unidirectional voltage.

2. In combination, an alternating current supply line, a dynamo electric machine connected thereto, a saturable reactor' in circuit with a winding of said machine and having 'a control winding, an electron tube connected in circuit with said supply line and said control winding and having a grid and means'to control the current in said control winding in accordance with a characteristic of said machine, said means comprising means to supply a unidirectional rel.-

' erence voltage to said grid, also means to supply a second unidirectional voltage to said grid which is a function of said characteristic of said machine and which is opposed to said reference voltage, and also means to superimpose an alternating voltage of the frequency of the voltage of. said supply line and of a given phase relative thereto upon the resultant of said reference volt age and said second unidirectional voltage.

means comprising means to supply a unidir'eca tional reference voltage to said grid, also means to supply a second unidirectional voltage to said srid which is a function of said characteristic of said motor and which is opposed; to said reference voltage, and also means to superimpose an alternating voltage of the frequency of said supply and of a given phase relative to its voltage upon the resultant of said reference voltage and said second unidirectional voltage.

4. In combination, an alternating current supply, a motor supplied thereby, a saturable reactor in circuit with a winding of said motor andhaving a control winding, an electron tube connected in circuit with said supply and said control winding and having a grid, and means to control the current in said-control winding in accordance with the speed of said motor, said means comprising means to supply a unidirectional reference voltage to said grid. also means to supply a second unidirectional voltage to said grid which is a function of the counter-electromotive force of said motor and which is opposed to said reference voltage. and'also means to superimpose an alternating voltageof the frequency ofsaidsupplyandofagivenphaserelativetoits vol age upon the resultant of said reference voltageandsaidundirectionalvcltlge.

- to said supply and adapted to supply a unidirectional reference voltage to said grid, also means to supply a second unidirectional voltage to said grid which is a function of the counter-electromotive force of said motor and which is opposed to said reference voltage, and also means to superimpose an alternating voltage of the frequency of said supply and of a given phase relative to its voltage upon said reference voltage and said second unidirectional voltage.

6. In combination, an alternatim current supply, a motor supplied thereby, a saturable reactor in circuit with a winding of said motor and having a control winding, an electron tube connected in circuit with said supply. and said control winding having a grid, and means to con trol the current in said control winding in accordance with the speed of said motor, said means comprising the means to supply a unidirectional reference voltage to said grid, a rectifying circuit connected to a winding of said motor and adapted to supply a second unidirectional voltage to said grid'which is a function of the speed of said motor and which is opposed to said reference voltage, and also means to superimpose an alternating current voltage of the frequency of said supply and of a given phase relative to its voltage upon the resultant of said reference voltage and said second unidirectional voltage.

7. In combination, an alternating current supply, a motor supplied thereby, a saturable reactor in circuit with a winding of said motor and voltage.

having a control winding. an electron. tube connected in circuit with said supply and said control winding having a grid. and means to control the current in said control winding in accordance with the speed of said motor, said .means comprising a rectifying circuit connected to said simply and adapted to supply a unidirectional reference voltage to said grid, and also a rectifying circuit connected to a winding of said motor and adapted to supply a second unidirectional voltage to said grid which is a function of the speed of said motor andwhich is opposed to said reference voltage, and also means to superimpose an alternating voltage of'the frequency of said supply and of a given phase relative toits voltage upon the resultant of said reference voltage and said second unidirectional voltage.

8. In combination, an alternating current sup ply line, an induction motor supplied thereby, a saturable reactor in circuit with a winding of saidmotor and having a controlwinding, an electron tube connected in circuit with said supply and said control winding and having a grid and means to control the current in said control winding in accordance with the speed of said motor, said means comprising a rectifying circuit connected to said Supply and adapted to supply a unidirectional reference voltage to said grid, also a rectifying circuit connected to said winding of said motor and adapted to supply a second unidirectional voltage to said grid which is a func tion of the speed of said motor and which is apposed to said reference voltage, and also means to super mpose-an alternating voltage of the frequency of said supply and of a given phase relative to its voltage upon the resultant of said reference voltage and said second unidirectional CARROLL STANSBURY. 

